The present invention relates to an ultrasound diagnostic apparatus. The invention more particularly relates to an ultrasound diagnostic apparatus capable of suppressing heat generation from an ultrasound probe while easily controlling the ultrasound transmission and reception in spatial compounding.
Ultrasound diagnostic apparatus using ultrasound images are put to practical use in the medical field.
In general, an ultrasound diagnostic apparatus includes an ultrasound probe (hereinafter referred to as “probe”) and a diagnostic apparatus body. In the ultrasound diagnostic apparatus, the probe transmits ultrasonic waves toward a subject and receives ultrasonic echoes from the subject. The diagnostic apparatus body electrically processes the reception signals received by and outputted from the probe to produce an ultrasound image.
So-called “speckle” (speckle noise/speckle pattern) is known as a factor that may deteriorate the image quality of an ultrasound image in the ultrasound diagnostic apparatus. Speckle is white spot noise caused by the mutual interference of scattered waves generated by numerous scattering sources which are present in a subject and have a smaller wavelength than that of an ultrasonic wave.
Spatial compounding as described in JP 2005-58321 A and JP 2003-70786 A is known as a method of reducing such speckle in the ultrasound diagnostic apparatus.
As conceptually shown in FIG. 34, spatial compounding is a technique which involves performing a plurality of types of ultrasound transmission and reception in mutually different directions (at mutually different scanning angles) between a piezoelectric unit 100 and a subject, and combining ultrasound images obtained by the plurality of types of ultrasound transmission and reception to produce a composite ultrasound image.
More specifically, in the example shown in FIG. 34, three types of ultrasound transmission and reception are performed which include the ultrasound transmission and reception as in the normal ultrasound image generation (normal transmission and reception), the ultrasound transmission and reception in a direction inclined by an angle of θ with respect to the direction of the normal transmission and reception, and the ultrasound transmission and reception in a direction inclined by an angle of −θ with respect to the direction of the normal transmission and reception.
An ultrasound image A (solid line) obtained by the normal transmission and reception, an ultrasound image B (broken line) obtained by the transmission and reception in the direction inclined by the angle of θ, and an ultrasound image C (chain line) obtained by the transmission and reception in the direction inclined by the angle of −θ are combined to produce a composite ultrasound image covering the region of the ultrasound image A shown by the solid line.
The probe making up the ultrasound diagnostic apparatus includes a piezoelectric unit which transmits ultrasonic waves to a subject, receives ultrasonic echoes generated by reflection of the ultrasonic waves on the subject and outputs the received ultrasonic echoes as electric signals (reception signals).
Recently, the probe may also be provided with an integrated circuit board for use in amplifying the reception signals outputted from the piezoelectric unit, performing A/D conversion or other processing, changing the timing of transmission and reception of ultrasonic waves in the piezoelectric unit, wireless communication with the diagnostic apparatus body without using any cord, and reducing noise.
As is well known, the piezoelectric unit generates heat through the ultrasound transmission and reception.
Higher-definition ultrasound images are obtained with increasing power of ultrasonic waves transmitted from the piezoelectric unit. However, the amount of heat generated from the piezoelectric unit is also increased with increasing power of ultrasonic waves transmitted from the piezoelectric unit.
The integrated circuit board also generates heat through reception signal processing.
That is, the probe generates heat through ultrasound transmission and reception.
The heat generation from the probe destabilizes the drive of the piezoelectric unit and the operation of each circuit of the integrated circuit board. As a result, output signals from the transmitted or received ultrasonic waves are destabilized to further destabilize the signal processing in the integrated circuit board. That is, the heat generation from the probe lowers the image quality of ultrasound images.
Therefore, it is necessary in the ultrasound diagnostic apparatus to suppress the temperature increase within the probe as much as possible in order to consistently obtain high-definition ultrasound images.
As also described above, spatial compounding enables speckle on the resulting ultrasound image to be reduced.
On the other hand, since the directions of ultrasound transmission and reception are to be changed for each ultrasound image used to produce a composite ultrasound image, the control of ultrasound transmission and reception becomes complicated.